The invention relates to chemical mechanical planarization (CMP) of semiconductor wafer materials and, more particularly, to CMP compositions and methods for polishing copper interconnects from semiconductor wafers in the presence of dielectrics and barrier materials.
Typically, a semiconductor wafer is a wafer of silicon with a dielectric layer containing multiple trenches arranged to form a pattern for circuit interconnects within the dielectric layer. The pattern arrangements usually have a damascene structure or dual damascene structure. A barrier layer covers the patterned dielectric layer and a metal layer covers the barrier layer. The metal layer has at least sufficient thickness to fill the patterned trenches with metal to form circuit interconnects.
CMP processes often include multiple polishing steps. For example, a first step removes excess interconnect metals, such as copper at an initial high rate. After the first step removal, a second step polishing can remove remaining metal that remains on the barrier layer outside of the metal interconnects. Subsequent polishing removes the barrier from an underlying dielectric layer of a semiconductor wafer to provide a planar polished surface on the dielectric layer and the metal interconnects.
The metal in a trench or trough on the semiconductor substrate provides a metal line forming a metal circuit. One of the problems to be overcome is that the polishing operation tends to remove metal from each trench or trough, causing recessed dishing of such metal. Dishing is undesirable as it causes variations in the critical dimensions of the metal circuit. To reduce dishing, polishing is performed at a lower polishing pressure. However, merely reducing the polishing pressure would require that polishing continue for a lengthened duration. However, dishing would continue to be produced for the entire lengthened duration. What is needed is a method to reduce dishing of metal in trenches or troughs without lengthening the duration of the polishing operation. Polishing compositions that leave a surface clear of interconnect metal residue after a short second step polishing time are needed.
U.S. patent application Ser. No. 2003/0219982 A1 mentions in a general way that cellulose might be used as a protective film forming agent or a water soluble polymer in polishing compositions for use on metals. Specific concentrations and cellulose properties are not disclosed in this reference. There is a need for polishing compositions that provide low dishing while providing adequate metal residue clearing.